1. Field of the Invention
The present invention generally relates to the transmission of data from energy meters to a communication device external the meter, and more specifically, relates to avoiding the loss of data during transmission of such data over a communication medium.
2. Related Art
Transmitting data via radio, telephone, and power line communication links is well known. In addition, transmitting data from an energy meter disposed at a customer location to a central station via such communication links is well-known. Examples of such systems utilizing power-line/radio links are described in U.S. Pat. Nos. 3,702,460 and 4,749,992.
Transmitting metering data over such communication links, however, can present many challenges. Although communication technology has now progressed to being very reliable, there still exists a possibility for transmission problems. For example, it is possible that the transmitted data may not be correctly received by a receiver or possibly even lost during transmission. For some data-types (e.g., watthour readings), if the data is lost, another attempted transmission can be made. This is possible because the watthour data typically is retained in the meter memory and not erased.
Other types of meter data, however, typically are erased from meter memory immediately subsequent to reading such data. One type of such data is commonly known as "Maximum Demand." Demand is "It]he average value of power or related quantity over a specified interval of time" and maximum demand is "[t]he highest demand measured over a selected period of time, such as one month." Handbook of Electricity Metering, Edison Electric Institute, Washington, D.C., Eight Edition (1981). As an example, a demand interval may be defined as thirty minutes and the maximum demand time period may be defined as one month. The maximum demand would be the highest demand measured during any thirty minute interval of the month.
When reading a demand meter, the maximum demand value is read and then immediately reset to zero. The maximum demand data therefore is immediately erased after reading. Resetting maximum demand cannot be delayed because if a maximum demand occurs between the time of reading and reset, the maximum demand for the previous time period is erased, i.e., replaced by the new maximum demand.
With human meter readers, where the reading is taken visually from a display on the meter, the meter reader can record the data and even double-check the data before resetting. When reading the data remotely, however, such as via a radio/power-line communication link, the maximum demand value is re-set once the data is transmitted. If the maximum demand data is lost during transmission, the data cannot be retrieved. Losing such data, of course, is not acceptable to the utility industry. Accordingly, there exists a need to provide a means and a method for storing data (e.g., maximum demand data) while remotely reading a meter.